The present invention relates to electronic devices, and more particularly to a semiconductor device adapted to sustain high voltages.
In electronic systems, there is often a need to sustain a relatively high voltage across a pair of nodes. Semiconductor p-n junction diodes are widely used in a reverse-bias mode to sustain high voltages. To sustain a high breakdown voltage across a p-n junction, a lightly doped region is required that is relatively thick and that forms a voltage sustaining layer. Such p-n junctions provide relatively higher breakdown voltage in many semiconductor devices such as MOSFETs, IGBTs and JFETs. Moreover, such semiconductor devices are typically required to have a relatively low on-resistance (Ron) in the on-state and a relatively high breakdown voltage VB under reverse bias conditions. As is well known, achieving both a high breakdown VB and a low Ron poses a number of challenging tasks. In conventional devices, design parameters such as the doping density or layer thickness that can be used to increase the breakdown voltage causes the on-resistance to increase, and vice versa.
One known device used to achieve both a low on-resistance as well as a high breakdown voltage is commonly referred to as the SuperJunction (SJ) device. As is shown in FIG. 1, a SJ device (structure) often includes a number of alternating p-type and n-type layers or pillars that are charge balanced. In a SJ structure, it is desirable to pack as many pillars or cells in a given unit area to lower the specific on-resistance, Rsp, which is defined as Ron*A, where A is the device area.
In a SJ structure, the widths of the n-type and p-type pillars set a limit on the cell pitch and the scaling down of the structure. There are also a number of drawbacks associated with the manufacturing of a SJ structure, such as the requirement to grow multiple epitaxial layers and to perform a number of implant and diffusion steps. A need continues to exist for a semiconductor device that has a high breakdown voltage, a low Rsp, low capacitances and low reverse recovery charge (Qrr), is easily scaled down and is easier to manufacture.